Saturday, June 23, 2012

We see quite a few hummingbirds in our yard. They are among my favorite things to watch - they are pretty fearless, and will come right up to us. I expect because they want us to get out of their territory. They haven't learned much about sharing yet.

Hummingbirds are among the smallest of birds, most species measuring in the 3–5 inch range. They can hover in mid-air by rapidly flapping their wings 12–80 times per second (depending on the species). To conserve energy while they sleep or when food is scarce, they have the ability to go into a hibernation-like state (torpor) where their metabolic rate is slowed to 1/15th of its normal rate. They are also the only group of birds able to fly backwards. They can fly at speeds exceeding 34 mph!

Hummingbirds drink nectar, a sweet liquid inside certain flowers. Like bees, they are able to assess the amount of sugar in the nectar they eat; they reject flower types that produce nectar that is less than 10% sugar and prefer those whose sugar content is stronger. Nectar is a poor source of nutrients, so hummingbirds meet their needs for protein, amino acids, vitamins, minerals, etc. by preying on insects and spiders.

Hummingbirds drink by using protrusible grooved or trough-like tongues. Hummingbirds do not spend all day flying, as the energy cost would be prohibitive; the majority of their activity consists simply of sitting or perching. Hummingbirds feed in many small meals, consuming many small invertebrates and up to twelve times their own body weight in nectar each day. They spend an average of 10–15% of their time feeding and 75–80% sitting and digesting.

With the exception of insects, hummingbirds while in flight have the highest metabolism of all animals, a necessity in order to support the rapid beating of their wings. Their heart rate can reach as high as 1,260 beats per minute! They also consume more than their own weight in nectar each day, and to do so they must visit hundreds of flowers daily. Hummingbirds are continuously hours away from starving to death, and are able to store just enough energy to survive overnight.

Hummingbirds are for the most part unsociable. In fact, the adjectives pugnacious and feisty are often appropriate. When more than one hummingbird is around, it is often a scene of repeated high-speed chases. In fact, male and female hummingbirds do not form a pair-bond after mating and the female is left to care for eggs and chicks alone.

Hummingbirds do not need the help of other hummingbirds, either to locate food or fend off predators. Other hummingbirds are competitors for the flower nectar upon which they thrive. The help that a male might provide a female does not outweigh the burden of having a male around competing for food.

What is all this fighting about? Plants take time to secrete nectar into their flowers. In an ideal world, hummingbirds should time their visits to flowers to take advantage of a full load. But they wait to feed at a flower at the risk of other hummingbirds beating them to the punch. It is therefore worth the effort for hummingbirds to chase away competitors so they have access and control of their favorite flowers.

In many cases, hummingbirds defend small territories around a favorite flower patch, and do so even during brief stop-overs for refueling during migration. Where many species live together, the large species attempt to dominate flowers and get the biggest drinks of nectar and smaller species try to sneak in for a few sips.